Device for delivering drug to certain pH environments

Claim 1

An oral osmotic device for the delivery of a beneficial agent to the stomach as a first environment of use and to the intestine as a second environment of use, the device comprising: (a) a shaped wall formed of (1) a semipermeable material that is permeable to the passage of an exterior fluid, substantially impermeable to the passage of agent, and maintain its physical and chemical integrity in both the first and second environment, said semipermeable material a member selected from the group consisting of a cellulose ester, cellulose ether, cellulose ester-ether, cellulose acylate, cellulose diacylate, cellulose triacylate, cellulose acetate, cellulose diacetate, cellulose triacetate, and cellulose diesters, and blended therewith (2) a pH sensitive material that is permeable to the passage of an exterior fluid, substantially impermeable to the passage of agent, maintains its physical and chemical integrity in the first environment and loses its physical and chemical integrity in the second environment, said material a member selected from the group consisting of cellulose carboxylic acid ester, cellulose carboxylic acid ether, cellulose ethyl phthalate, cellulose acetate phthalate, starch acetate phthalate, amylose acetate phthalate, hydroxypropyl methylcellulose phthalate, hydroxypropyl ethylcellulose phthalate, hydroxybutyl methylcellulose phthalate, cellulose acetate hexahydrophthalate, and hydroxypropyl methylcellulose hexahydrophthalate; (b) a compartment containing a dosage unit amount of a beneficial agent; (c) a passageway through the wall connecting the compartment with the exterior of the device, the passageway having a maximum cross-sectional area, A s defined by ##EQU3## wherein L is the length of the passageway (Q p /t) is the mass delivery rate of the agent, D is the diffusion coefficient of agent, S is the solubility of agent in the fluid, and F is from 2 to 1000, said passageway having a minimum area A s defined by ##EQU4## wherein L is the length of the passageway, v/t is the agent solution volume delivery rate, π is 3.14, ηis the viscosity of the agent solution dispensed from the osmotic device, and ΔP is the hydrostatic pressure difference between the inside and the outside of the compartment having a value up to 20 atmospheres; and (d) wherein, when the osmotic device is in the first environment, the device maintains its integrity and delivers agent through the passageway at a controlled rate over a prolonged period of time, and when the device is in operation in the second environment, the device loses its integrity and delivers the remaining agent in a short period of time.